In many cases, treatment of an object or a region formed by the object and the medium surrounding the object, such as ballast water and ballast water treatment systems, is necessary in order for treatment effects to be carried out, such as controlling the transportation of undesirable and invasive marine organisms.
Ballast water is water that is pumped in and out of ballast tanks in vessels to regulate stability, increase draft or otherwise provide ballasting action to the vessels. To control the transportation of unwanted invasive marine organisms by foreign-going vessels in such ballast water, the International Maritime Organization (IMO) and USCG implement regulations on ballast water treatment. The general control requirement specified by IMO is given as follows:
OrganismsMax allowable at discharge>50 μm<10 per cu.m10~50 μm<10 per mlToxicogenic Vibrio Cholera <1 cfu/100 mlEscherichia coli<250 cfu/100 mlIntestinal Enterococci<100 cfu/100 ml
In general, present ballast water treatment systems available in the market all approach treatment by a conventional disinfection concept, which uses methods such as chlorination, UV treatment, use of radicals, etc. However, none of these disinfection methods solve the problems in a complete, or holistic, manner. All the technologies available in the market focus on how to kill the organisms in the water but they have not been able to eradicate the organisms living in sediment in the tanks or underneath corroded steel areas.
The most common ballast water treatment disinfection technologies used in large scale applications can be broadly classified as follows:                1. Electro-chlorination (using active substances);        2. UV disinfection systems (without using active substances);        3. Combining Fine filter/UV/AC Ultra Low Frequency avalanche current (without using active substances)        
Despite being the most commonly used large scale disinfection systems in the marine industries, these systems have many shortcomings.
The electro-chlorination system uses a DC electrolysis system to electrolyze seawater to produce chlorine/hypochlorite for disinfection or to kill the organisms in the water. Organisms that are greater than 50 μm in a major dimension are usually pre-removed by either cyclone separators or mechanical mesh filters. Organisms that are smaller than 50 μm are then disinfected or killed by the active substance such as chlorine/hypochlorite. In the process of electrolysis, toxic chlorine and explosive hydrogen gas are inevitably generated which is one of the major shortcomings of these systems.
Another issue with the electro-chlorination system is that the amount of oxidizing agent and active substances produced are harmful to the environment. The oxidizing agent amount is usually measured by the total residual oxidants (TRO) present in the water. Depending on the type of water and also the organisms present, the amount of TRO required by an electro-chlorination system for control of organisms in water is in general more than 10 ppm. However, water with such a high dosage of TRO is also harmful to the environment and cannot be discharged directly without further treatment to reduce the TRO.
A further issue is that such high TRO levels cause severe corrosion to the metallic structures and equipment in the piping system and they may also affect the material integrity of some non-metallic structures. For environmental reasons, statutory requirements usually require the discharge water TRO be further treated to 0.2 ppm or less. To meet this requirement, dosing with a TRO reducing agent before discharge will be needed, which is a further disadvantage for electro-chlorination systems.
For effective control of organisms in a ballast water system, it is critical that bio-film sites are controlled or eradicated, instead of just focusing on the kill rate of the organisms in the bulk water. In electro-chlorination systems, chlorine and hypochlorite are effective in killing the organisms in bulk water but have very limited success in penetrating the biofilm to kill the bacteria and organisms living inside the system. Obviously the corrosion on the steel surface caused by the TRO creates more corrosion sites which are unreachable by the disinfectant, which then compromises the disinfection efficacy.
Yet another issue with the chlorination system is the control of re-growth of phytoplankton. Phytoplankton can re-grow very quickly after the chlorination treatment effect subsides if the nutrients and correct growth environment exist. Therefore if chlorine-treated ballast water is kept in the ballast tank for a long period of time the phytoplankton may still survive and hence be introduced to another country, even though the water is deemed to have been treated. This problem is especially common for ballast water treatment systems which only treat the ballast water as part of the ballasting cycle but not at de-ballasting.
Yet another shortcoming for the electro-chlorination system is the natural chloride content of the water being used for ballasting. If the chloride content is low, such as in estuary or river water, the amount of chlorine and hypochlorite generated may be too low for effective disinfection. Some systems resort to using another tank to carry seawater to then electrolyze the seawater for injection into the fresh water for disinfection but this reduces the cargo capacity of the ship.
The shortcomings of the electro-chlorination system can be summarized as follows:                1. Generation of explosive hydrogen gas;        2. Corrosion issue due to high TRO;        3. TRO reduction treatment is required after treatment;        4. Bio-organisms may be immune to chlorination;        5. Inability of chlorine to penetrate biofilm to eradicate organisms living in biofilm;        6. Inability to control re-growth of phytoplankton after treatment;        7. Unable to provide effective disinfection if chloride content in water is low        
UV disinfection treatment technology uses the UVC range of UV light to disinfect the water. Some may use UVA and UVB in conjunction with UVC for disinfection but the concept and methods are same. When UV is used for disinfection, there are also many disadvantages.
UV treatment is effective only at the point of treatment and it does not have a residual effect to carry the treatment effect through the whole system. When the treatment system lacks a residual treatment effect, those organisms and bacteria not killed at the point of treatment or left in the piping systems, including the tank, will be able to grow and multiply again leading to a poor overall disinfection result.
Since UV does not have a residual effect, the effect cannot be carried by the treated water to eradicate the biofilm. This results in the growth of organisms or ineffective disinfection.
The general concept is that UV does not induce any corrosion problems but in actual ballast seawater treatment, the very strong UV dosage used for the disinfection functions can cause the TRO in the water to rise. In some extreme case, the increase in TRO by very strong UV can reach as high as 0.5 ppm especially with the present of TiO2. Not only does this exceed the discharge water TRO requirement, but the residual oxidants also accelerate the corrosion rate of the immersed metallic structures. This in turn creates a chain effect of creating more habitats for the organisms, which then need higher dosages of disinfection, which then result in more TRO and hence more corrosion.
Many UV ballast systems rely on very fine filters to filter off the >50 μm organisms and then use UV to kill the <50 μm organisms, including bacteria. While UV can provide effective disinfection with good killing and control of the bacteria count in bulk water, it is less efficient in killing larger organisms. For organisms larger than bacteria, the strength of the UV required to kill them is very high, especially for phytoplankton, and hence the power consumption of such systems will also be high. As a result, the power consumption for many types of UV system for ballast water treatment is very high. Using LED UV may reduce the power consumption, but the cost of LED UV is, itself, extremely high. Regardless of whether low, medium or high pressure UV lamps are used, the power consumption is so high that for large ballasting capacity vessels, it may be necessary to install additional generators onboard to provide the extra power and in many cases this is not practical.
The effect of water conditions also affects the efficacy of UV treatment. The strength of the UV light is greatly affected by the water turbidity as well as by fouling conditions on the UV lamp quartz sleeve which is in contact with water. Under high silt content and turbid water conditions, such as in ports, river water or estuary water, it is very difficult for the UV light to penetrate through the turbid water which then compromises the disinfection efficacy. Currently there is no filtration system in the market that is able to filter the silt effectively under the large flow conditions required for ballast water treatment. If the water turbidity issue is not resolved, the application of UV in turbid water is not practicable.
In addition to water turbidity, fouling on UV lamp quartz sleeves will cause the UV treatment efficacy to deteriorate further. Using chemicals or brushes to clean the fouling adds to operating and equipment costs, although they may help to maintain the treatment efficacy to a certain extent.
The third type of treatment combines fine filters with UV and AC Ultra Low Frequency avalanche currents. These require very high performance fine filters of <50 μm mesh to remove the larger organisms to maintain the effectiveness of the disinfection. This is due to the fact that the UV+ pure AC ULF treatments are less effective in treating larger organisms unless extremely high power is used. Should the filter mesh or seals develop leakage during operation, large organisms will pass through the filter and enter the UV and ULF chamber directly. This can then affect the UV+ULF treatment such that it is not able to meet the larger organism disinfection requirements.
Another drawback with the UV+ULF treatment is that it requires two separate processes to produce effective disinfection control. Without the UV, the ULF treatment itself will not be able to meet stringent marine ballast water treatment requirements even though the ULF treatment has a disinfection effect. In ballast water treatment, the disinfection requirement requires the full disinfection effect to take place on the day of deballasting after treatment for bacteria, 10˜50 μm organisms and >50 μm organisms. ULF treatment alone will take more than two days to meet this deballasting discharge requirement unless the ULF strength is increased substantially. Alternatively, a UV system may be added to supplement the ULF disinfection treatment effect, especially on the total bacteria count, to ensure it meets the disinfection count requirement by the second day. However, once the UV system is incorporated into the ULF system, the shortcomings of the UV system noted above are also relevant to the combined UV+ULF system.
Yet another issue with a pure AC ULF system is that the avalanche current can only be produced in a non-metallic chamber or pipe section. Hence for application in a metallic ballast water system, a non-metallic pipe section needs to be added into the steel ballast water pipes, and these non-metallic sections may not be sufficient for applications that require high pressures and/or to satisfy explosion-proof safety requirements.
The above mentioned technical issues regarding Ballast Water treatment requirements are referring to IMO (International Maritime Organization) requirements. The latest United States Coast Guard USCG ballast water treatment requirement which came in force in early 2016, imposed a much more stringent requirement on 10˜50 um phytoplankton organism disinfection than the IMO requirement.
The IMO requirement accepts the 10˜50 um phytoplankton count after treatment by the so called “Most Probable Number” MPN count number. That is the phytoplankton although not killed immediately after the treatment is allowed to go through 14 days of “regrowth” period. Should the phytoplankton be unable to multiply in these 14 days and the total number is remaining at less than 10 per ml, it is considered as passed by IMO standard.
For the new USCG requirement, no MPN is allowed to be used for counting the phytoplankton. The phytoplankton must be totally “dead” after holding for a period as specified in the test. The holding days are usually less than 5 days. By totally “dead” is meant not only that the phytoplankton organism cannot multiply, but also that there should be no detectable metabolic activity in the phytoplankton cell.
With this new totally “dead” requirement, the conventional UV system will need to add on at least 4 to 5 times more power to the already very high, impractical power consumption characteristic. This makes the conventional UV system totally impractical for shipboard application.
For the UV+pure AC ULF system, the same situation as conventional UV arises although the power consumption increase is less than in the case of conventional UV.
The listing or discussion of an apparently prior-published document in this specification should not necessarily be taken as an acknowledgement that the document is part of the state of the art or is common general knowledge.
It has been always a challenge to develop alternative technologies for obtaining various treatment effects that are effective, cause no harm to the environment and yet are able to meet the latest most stringent USCG requirement. Therefore, there is a need for new methods and systems that are capable of carrying out effective disinfection of ballast water and meeting the most challenging USCG 10˜50 urn phytoplankton treatment requirement without causing harm to the atmosphere or aqueous environments.